1. Field of the Invention
The present invention relates to a steering system in a wheeled vehicle, and more particularly to a four-wheel steering system in a wheeled vehicle the front wheel steering mechanism of which is drivingly interconnected to a rear wheel steering mechanism to steer the rear road wheels in either the same or the opposite direction as the front road wheels in dependence upon the turn-angle of the steering wheel of the vehicle.
2. Description of the Prior Art
In such a four-wheel steering system as described above, a linkage such as a rotary shaft assembly is arranged in a fore-and-aft direction of the vehicle and drivingly connected at its front end to a front wheel steering mechanism to be rotated in response to operation of a steering wheel, and a connecting mechanism is assembled in combination with a rear wheel steering mechanism to drivingly connect the linkage to an operation rod of the rear wheel steering mechanism in such a manner that the operation rod is displaced in an axial direction in response to rotary motion of the linkage to steer a pair of dirigible rear road wheels in either the same or the opposite direction as a pair of dirigible front road wheels in dependence upon the turn-angle of the steering wheel.
In Japanese Patent Early Publication No. 61-9374, there has been proposed such a connecting mechanism adapted for use in combination with the rear wheel steering mechanism, wherein the connecting mechanism includes a housing mounted on a vehicle body structure for axially slidably supporting thereof an opertion rod, an input shaft rotatably mounted within the housing and in drive connection to the linkage for rotation therewith, the input shaft being integrally formed at its rear end with an eccentric shaft, a cylindrical member rotatably mounted on the eccentric shaft, the cylindrical member having a pinion formed on its front portion and an eccentric cam formed on its rear portion, a stationary cylindrical member positioned in place in the housing in surrounding relationship with the pinion, the stationary cylindrical member being formed with an internal ring gear in mesh with the pinion, a pair of vertical guide members secured to one side of the operation rod, and a slider rotatably mounted on the eccentric cam and slidably supported by the guide members to effect axial movement of the operation rod in accordance with rotary motion of the eccentric cam. In operation of the connecting mechanism, the slider is applied with a resultant force caused by revolution and rotation of the eccentric cam, and the operation rod is displaced by a lateral component of the resultant force applied thereto from the slider to steer the rear road wheels.
For application of the connecting mechanism to various kinds of vehicles, the ratio of the rear wheel steering angle relative to the front wheel steering angle can be adjusted by selection of the gear ratio between the pinion and internal ring gear and the eccentric amount of the cam. The selection of the gear ratio in a limited space is, however, restricted due to limitation of each module of the gears. For this reason, it is very difficult to define an optimum steering angle of the rear road wheels relative to the front road wheels for each performance of the vehicles. During assembly process of the connecting mechanism, it is required to couple the slider over the eccentric cam in a condition where the input shaft, the eccentric shaft, the eccentric cam and the internal ring gear are aligned at each center thereof on a common vertical line. This means that precise assembly of the component parts is required, resulting in an increase of the manufacturing cost of the mechanism.